I think he's right. Run PostgreSQL on the centos host directly, rather than from within a guest. The vm guests could access the database over the virtual lan, so speed of access for guests on the same server wouldn't be an issue. There are lots of ways of file sharing for example. You can share from within a linux or windows guest, or you could share directly from the centos host with samba or iSCSI. I get native speeds from guests, but I think running directly from the server is always going to be faster.